Many hand-held lasers are used as laser pointers in lecture rooms, laser shows and various laser games. In some cases these lasers are used for intentional dazzling of eyes and optical sights. These lasers have several specific wavelengths, such as a 535 nm wavelength green laser, the second harmonic of the widely used Neodymium laser and other lasers in the red and the blue ranges.
Many lasers have powers that are permanently or temporarily damaging to the eye and/or various electronic sensors. These lasers can impinge on the sensor from various directions and angles. In order to shield against them, a safety filter is needed to protect the eye and/or sensor.
The conventional solution for a wavelength-specific filter is a thin film interference filter. These filters are strongly dependent on the specific angle of impingement of the damaging light. Moreover, these filters do not transmit light in a wide spectral band around the designed wavelength, to accommodate for the angles of impingement that are not perpendicular to the surface. Thus, the use and applicability of these filters are limited. Thin film interference filters designed to block three known wavelengths, e.g., blue, green and red, at angles up to 30° will allow only about 30% of the visible light to pass and thus will result in a poor image.
Prior work has dealt with high-power lasers. For example, an optical limiter, Israeli Patent 147554, describes various ways to realize a limiting device. Other examples include EP1467238 and application JP2004-115104 and patents disclosed in them, teaching on an optical power limiter that is based on thermally changed scattering effect of an element that combines a mixture of particles in a matrix.
There is an unaddressed need in the art for an impingement angle-independent, wavelength-specific limiter for these applications. The present disclosure addresses these needs and provides a limiter, designed for a plurality of specific wavelengths.
Up-conversion refers to nonlinear optical processes characterized by the successive absorption of two or more pump photons via intermediate long-lived energy states followed by the emission of the output radiation at a shorter wavelength than the pump wavelength. Since then, conversion of infrared radiation into the visible range has generated much of the interest in up-conversion research. The knowledge gained thus far has allowed the development of effective optical devices such as infrared quantum counter detectors, temperature sensors, and compact solid-state lasers. Despite its remarkable potential utility, the practical use of up-conversion has been extremely limited.
Nanoscale manipulation, e.g., of lanthanide-doped up-conversion nano-crystals, leads to important modification of their optical properties in excited-state dynamics, emission profiles and up-conversion efficiency. For example, the reduction in particle size provides the ability to modify the lifetime of intermediate states. The control of spatial confinement of dopant ions within a nano-scopic region can lead to marked enhancement of a particular wavelength emission as well as generation of new types of emissions.
In many applications, there is insufficient UV and short wave visible light radiation to actuate the photochromic material. The addition of up-conversion materials enables the in-situ generation of UV and/or short wave visible light that in turn can trigger photochromic materials and devices in these applications.
The current disclosure relates to absorption of impinging angle-independent laser light in up-converting materials, and the use of the re-emitted light to tint a photochromic dye, which in turn can limit the transmission of the exciting laser.